During operation, an aircraft turbine engine releases a significant quantity of heat. The heat arises from the air compression and combustion, but also from friction in the gears of the power transmission units and in the bearings. The multiplicity of electrical equipment further increases this heating. It is also noted that certain operating phases, such as take-off, create additional heat.
The heat is transported from the heat sources to exchangers via a circuit using a heat-transmitting fluid. The lubricating oil is ideal for this function since it comes closely into contact with the hot sources and is then collected. Cooling typically takes place by the addition of an exchanger in which the collected oil circulates.
Typically, part of the heat is recovered for the useful functions of the aircraft such as defrosting, fuel preheating, cabin heating etc. The surplus heat is dissipated into the atmosphere via exchangers which transfer the heat from the heat-transmitting fluid to the air. The cooling performance is variable, depending on such things as the temperature difference between the heat-transmitting fluid and the air. Cooling may become critical in desert areas where the air temperature, expected to form a cold source, reaches 50° C. In addition, the thermal capacity of air is low.
Document US 2009/0007570 A1 discloses an axial turbine engine for an aircraft. The turbine engine comprises a turbine and a compressor which are lubricated by an oil circuit. Utilizing a heat exchanger, the circuit also allows cooling of the oil following the heating it undergoes while performing its lubrication function. The exchanger uses the air of the secondary flow passing through the turbine engine as a cold source. This arrangement benefits from a significant flow of incoming air and allows consequent cooling.
However, the cooler is bulky. In fact a cooler is normally dimensioned to meet the maximum need, taking into account certain operating margins and the possibility of incidents. Such a cooler becomes heavy and increases the drag of the turbine engine.